Pests infestations are the undisputed nemesis of indoor and outdoor gardeners alike. Often seemingly appearing from nowhere, they can quickly cause devastation and destruction to our beloved plants if left untreated. Whiteflies are some of the most common houseplant pests, taking advantage of the warm indoor climate and plentiful foliage to feast on.
These little white bugs are more than just a nuisance, they can cause considerable damage, and the fact that their wings offer an easy escape route means they can be a nightmare to eradicate. Luckily, with a little perseverance, and a thorough treatment regime, they are treatable, and whiteflies needn’t be a death sentence for your plants. This guide will teach you everything you need to know about whiteflies, and most importantly, how to get rid of them for good.
Whiteflies are small winged insects belonging to the Aleyrodidae family. There are over 1500 different known species of Whitefly. They generally grow to no more than two millimetres in length and their bodies are covered in a protective white-coloured dusty substance that looks like flour, which is how they get their name.
Whiteflies tend to congregate on the underside of leaves to feed and lay eggs. They lay their eggs in a spiral formation and each egg has a long, translucent stalk attached to it. Each female can lay up to two hundred eggs during their lifespan, and in warm temperatures, they are able to reproduce and repeat the lifecycle in as little as three weeks.
Whiteflies are polyphagous, meaning they feed on many different species of plant, so are prone to spreading quickly when different plants are kept together. They feed on the sap of the host plant, causing it to become gradually weaker, and they often transmit secondary diseases such as mosaic virus, as well as injecting the plant with their toxic saliva.
What Causes Whitefly Infestations?
Whiteflies love hot conditions, so your houseplants are especially vulnerable in the consistently warm temperatures of the home. Outdoors, whiteflies can’t withstand cold winter temperatures and become dormant, but indoors they remain active all year round. Since whiteflies have no natural predators indoors as they do outdoors, their populations can quickly get out of hand.
How to Prevent Whiteflies
Before purchasing any new houseplants, inspect them thoroughly to make sure they are healthy and free of pests. No matter how healthy they appear, it’s always a good idea to keep new additions isolated from your wider collection for at least four weeks. This should be enough time for any lurking pest populations to make themselves known before they have chance to infest any other plants.
It’s important to inspect all your houseplants regularly for any signs of pests or disease. Early detection can really boost your chances of successfully eradicating any unwanted visitors. Be sure to inspect the underside of the leaves, as this is where whiteflies and their eggs will usually assemble. Whiteflies are prolific, rapid breeders, and can fly between plants easily to spread their population, so the earlier you spot them, the sooner you can act. Healthy plants are also much more resilient to pest damage, so make sure that your plants are happy and their needs are met.
Try to promptly remove any dead or decaying plant matter which gathers on top of the soil, as these can still can provide food for lurking whiteflies.
Some gardeners believe that nitrogen-rich fertilisers can encourage whiteflies, so you may want to switch to a low-nitrogen food or reduce the frequency or strength of any food during the warmer months, when whiteflies are most active.
Whiteflies are averse to certain plants, particularly those with strong scents, you could to deter them by using a companion planting system. Positioning house-friendly herbs like basil, cilantro, mint, and sage in amongst your houseplants might help to keep the flies at bay.
Whiteflies and their eggs are usually large enough to see with the naked eye. It helps that they tend to congregate in large numbers, making them easier to spot, and they will often fly up in large swarms when an affected plant is disturbed.
Infested plants will often have tiny light marks or discolouration on the foliage where the insects have pierced the tissue to access the sap. The toxicity of the flies saliva can cause chlorosis, a lack of the natural green colouring that comes from chlorophyll. Without chlorophyll, plants are unable to photosynthesise properly, and their growth will become stunted. This, coupled with the depletion in nutrients as whiteflies consume sap, causes plants gradually become weaker, and the foliage to become yellowed, shrivelled, curled, and eventually drop. Because whitefly populations tend to get very large very quickly, the host plant can soon become overwhelmed, and an unchecked infestation can be fatal.
Like most sap-sucking pests, whiteflies secrete a sticky, sweet substance known as honeydew as they feed. The honeydew is relatively harmless in itself, but it can encourage fungal growths known as sooty mould. This black fungus spreads over the foliage, preventing the plant from photosynthesising efficiently, and causing it to become even weaker.
Whiteflies also inflict secondary damage to host plants since they carry and transmit a wide variety of viruses, most commonly different strains of mosaic virus. Look out for shrivelled leaves with mottled yellow marks and splotchy patterns.
How to Get Rid of Whiteflies
Like many other houseplant pests, whiteflies are known to quickly become resistant to many of the most common chemical and synthetic pesticides. It’s best to use a natural, organic approach to treat them. Additionally, when treating plants indoors, its always best to avoid using harmful chemicals that may have adverse effects on humans and animals living in the home.
You will probably need to employ two different methods of treatment, one to kill the immobile nymphs, and another to kill the flying adults. It’s also a good idea to repeat any treatment several times over the course of a few days or weeks, to be sure that the life cycle has been sufficiently disrupted.
As with all topical treatments, perform a test application on a small area of the plant first. Leave it for a couple of days to see if it causes any damage before applying to the whole plant. Additionally, try to avoid applying any liquid treatments during the middle of the day when the sun is brightest, as they can scorch the leaves.
Isolate and Prune
As with any pest or disease, the first, and most important, course of action is to isolate your plant so the problem can’t spread to other plants. This is especially important with any winged pest like whiteflies since they can easily fly from plant to plant.
Whiteflies tend to feed on one leaf at a time, moving onto the next when they have taken all the nutrients from the first. This makes it easier to identify and remove the worst affected leaves from the plant. Once removed, dispose of the cuttings carefully, making sure that the adults aren’t able to fly back to your plants again.
Rinsing or Vacuuming
Rinsing an affected plant under a steady, moderately powerful stream of clean water can help to dislodge whiteflies, their eggs, and nymphs. Pay special attention to the undersides of leaves. Don’t use this method on particularly delicate plants as the water pressure may damage them. Rinsing the plant will also help to get rid of any sooty mold which may have emerged as a result of the honeydew secretions.
Alternatively, you could use a vacuum to suck up the whiteflies, but be carful not to damage the plant as you work. You will need to dispose of the vacuum bag immediately afterwards to make sure that they aren’t able to fly back out again.
Yellow sticky traps
Whiteflies are attracted to the colour yellow, so sticky traps are a great way to kill adults. You can either use strips which are hung above the plants, or cards which can be inserted directly into the soil in the plants’ pot. Gradually, you will notice the traps fill up with whiteflies that have become stuck to the adhesive. This method is only effective with flying adults though, so will need to be used in conjunction with another method that targets the nymphs and eggs.
Insecticidal soap will kill whitefly eggs and nymphs on contact by permeating their exoskeleton, smothering them and causing them to dehydrate. Usually, however, adults will fly away when you start applying the soap, so it won’t be so effective on them.
You can purchase ready made insecticidal soap, or you can make your own at home by mixing one tablespoon of gentle, fragrance-free dish soap, one tablespoon of vegetable oil and one liter of water. You can either use a spray bottle or a cloth to apply the solution to the whole of the plant, paying special attention to the undersides of the leaves. Allow the solution to settle for several hours before rinsing the whole plant thoroughly with clean water.
Neem oil is an organic and non-toxic pest treatment which is obtained from the Azadirachta indica tree. It kills whitefly eggs and nymphs on contact by smothering and suffocating them. Neem oil is usually sold as a concentrate, so follow the dilution instructions on the packaging before applying to your plant. Using a spray bottle or cloth, coat each leaf and stem in a generous amount of the solution. Unlike insecticidal soap, theres no need to rinse neem oil off afterwards.
Neem oil will act quickly on the immobile nymphs and eggs, since they aren’t able to escape the solution, but won’t be so effective on the mobile adults, who can easily escape. The added benefit of using neem oil is that is has a residual effect, meaning it will continue to protect your plant from future invasions after the treatment. You can also apply it to plants periodically as a preventative measure, even when no pests are present.
Arachnophobes beware, this method may not be for everyone, but it is both effective and preventative. Friendly house spiders can be gently relocated to the vicinity of the host plants, and they will soon begin to trap adult whiteflies in their webs. Whilst this might not be the fastest method, the spiders will eat the flies, helping to keep the adult population at bay and disrupting their rapid lifecycle. They will also provide future protection, keeping potential populations of whiteflies at bay before they have chance to really take hold.
During the summer, when temperatures are warmer, you could also place houseplants outdoors during the day. Whiteflies’ natural predators such as ladybugs and lacewings will soon swoop in to feast on them, keeping their population at far more manageable levels. Just remember to bring your plant back indoors in the evening when the temperature drops.
Frequently Asked Questions
Here are a few of the most common questions that we get about whiteflies:
Are whiteflies harmful to humans or animals?
Whilst they may pose a threat to our plants, the good news is that whiteflies are not harmful or toxic to any humans or animals living in your home.
How long do whiteflies live?
The average life cycle of a whitefly is around three weeks. During the summer, eggs mature into adults much faster, meaning they can reproduce more rapidly. In the winter, eggs will mature more slowly, and the life cycle can take several months to complete. Because they are able to reproduce so quickly, without intervention, an infestation will be continuous and can grow exponentially, usually with all different stages of egg, nymph, and adult present at once.